TABLE OF CONTENTS

Page no

1. INTRODUCTION………………………………………………………………………….1

2. UNDERWATER WELDING……………………………………………………………2

2.1 CLASSIFICATION……………………………………………………………………..2

2.1.1 WET WELDING…………………………………………………………………….2

2.1.2 PRICIPLE OF OPERATION……………………………………………………..3

2.1.3 WORKING OF WET WELDING PROCESS………………………….......3

2.1.4 FUNDAMENTALS OF UNDERWATER WELDING…………………….4

2.1.5 REACTION CAUSED DURING WELDING………………………….......5

2.1.6 ENGINEERING MATERIALS USED FOR WET WELDING …………7

2.1.7 WELDING PROCESSS AND CONSUMABLES………………………….8

2.1.8 EQUIPMENTS FOR UNDERWATER WELDING……………………….9

2.1.9 ADVANTAGES AND DISADVANTEGES OF WET WELDING…….10

3. DRY WELDING (HYBPERBARIC WELDING)………………………………….11

3.1 DRY WELDING IN HABITAT……………………………………………………..12

3.2 DRY CHAMBER WELDING………………………………………………………..12

3.3 ADVANTAGES AND DISADVANTEGES OF DRY WELDING…………13

4. RISKS INVOLVED ………………………………………………………………………..14

5. APPLICATION OF UNDERWATER WELDING………………………….........15

6. SAFETY, DIVING ISSUES AND HAZARDS……………………………….........15

7. FURTHER DEVELOPMENTS IN UNDERWATER WELDING………..…….16

8. CONCLUSIONS AND REFERENCES………………………………………………..17

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LIST OF FIGURES

Figure no Description Page no

1 Working process of a wet welding 3

2 Fig shows person doing underwater welding in ocean

5

3 Tip of rutile underwater wet welding electrodes with double waterproof coating

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4 Underwater wet welding in the laboratory pool

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5 Underwater joint made with arc “spot” welding

9

6 Appearance of the welded sample 9

7 specially designed habitat for repair of K-nodeon offshore platform

12

8 Dry welding in minihabitat where the diver-welder is partially immersed in water

13

9 Arrengements of underwater welding 14

10 electrodes used in underwater welding 15

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1. INTRODUCTION

The fact that electric arc could operate was known for over a 100 years. The first ever

underwater welding was carried out by British Admiralty – Dockyard for sealing leaking ship

rivets below the water line. Underwater welding is an important tool for underwater

fabrication works. In 1946, special waterproof electrodes were developed in Holland by

‘Vander Willingen’. In recent years the number of offshore structures including oil drilling

rigs, pipelines, and platforms are being installed significantly. Some of these structures will

experience failures of its elements during normal usage and during unpredicted occurrences

like storms, collisions. Any repair method will require the use of underwater welding.

Underwater welding is an important tool for underwater fabrication works. In recent years

the number of offshore structures including oil drilling rigs, pipelines, platforms are being

installed significantly. Underwater wet welding technique was misunderstood for a long

time, and it was a synonym for low quality weld full of porosity and cracks with poor

mechanical properties like low ductility and due to micro structural issues prone to cracking.

This lack of experience and knowledge was present in companies which did not understood

all underwater welding issues which caused development of inadequate welding procedures,

poor welder technique and inappropriate filler materials. Through time, that status has been

changed, and today underwater welding projects, both dry and wet, are used in most complex

and difficult objects with a high level of quality assurance.

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2. Underwater Welding

It is the process of welding at elevated pressures, normally underwater. Underwater welding

can either take place wet in the water itself or dry inside a specially constructed positive

pressure enclosure and hence a dry environment. It is predominantly referred to as

“hyperbaric welding” when used in dry environment, and “underwater welding” when in a

wet environment.

2.1 CLASSIFICATION

Underwater welding can be classified as;

1) Wet Welding

2) Dry Welding

In wet welding the welding is performed underwater, directly exposed to the wet

environment. In dry welding, a dry chamber is created near the area to be welded and the

welder does the job by staying inside the chamber.

2.1.1 WET WELDING

Wet Welding indicates that welding is performed

underwater, directly exposed to the wet environment.

A special electrode is used and welding is carried out

manually just as one does in open air welding. The

increased freedom of movement makes wet welding

the most effective, efficient and economical method.

Equipment and other technical facilities are far more

complex and cheaper comparing to underwater dry

welding procedures so very often underwater wet

welding is proper technology to use for maintenance

of underwater structures and repair of ships.

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2.1.2 Principle operation of Wet Welding

The work to be welded is connected to one side of an electric circuit, and a metal electrode to

the other side. These two parts of the circuit are brought together, and then separated slightly.

The electric current jumps the gap and causes a sustained spark (arc), which melts the bare

metal, forming a weld pool. At the same time, the tip of electrode melts, and metal droplets

are projected into the weld pool. During this operation, the flux covering the electrode melts

to provide a shielding gas, which is used to stabilize the arc column and shield the transfer

metal. The arc burns in a cavity formed inside the flux covering, which is designed to burn

slower than the metal barrel of the electrode.

2.1.3 Working of wet welding processWelding power supply is located on the surface with connection to the diver/welder via

cables and hoses.In wet welding MMA (manual metal arc welding) is used.

Power Supply used : DC

Polarity : -ve polarity

When DC is used with +ve polarity, electrolysis will take place and cause rapid deterioration

of any metallic components in the electrode holder. For wet welding AC is not used on

account of electrical safety and difficulty in maintaining an arc underwater.

Fig 1; working process of a wet welding

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The power source should be a direct current machine rated at 300 or 400 amperes. Motor

generator welding machines are most often used for underwater welding in the wet. The

welding machine frame must be grounded to the ship. The welding circuit must include a

positive type of switch, usually a knife switch operated on the surface and commanded by

the welder-diver. The knife switch in the electrode circuit must be capable of breaking the

full welding current and is used for safety reasons. The welding power should be connected

to the electrode holder only during welding.

Direct current with electrode negative (straight polarity) is used. Special welding

electrode holders with extra insulation against the water are used. The underwater welding

electrode holder utilizes a twist type head for gripping the electrode. It accommodates two

sizes of electrodes.

The electrode types used conform to AWS E6013 classification. The electrodes must be

waterproofed. All connections must be thoroughly insulated so that the water cannot come in

contact with the metal parts. If the insulation does leak, seawater will come in contact with

the metal conductor and part of the current will leak away and will not be available at the arc.

In addition, there will be rapid deterioration of the copper cable at the point of the leak.

2.1.4 Physical fundamentals, weldability and metallurgical issues Wet underwater shielded electrode manual arc welding is characterized by the

following:

1. Electric arc instability, which causes irregular geometry in the welded joint, slag

inclusions, porosity and insufficient penetration. Ambient pressure has a significant

influence on the behaviour of a welding arc, the performance of the welding process

and the resultant weld properties. Increasing pressure leads to destabilisation of the

arc plasma resulting from escalating turbulence in the arc column.

2. The rapid cooling leads to great hardness in the heat-affected zone, low toughness in

the welded joint and the appearance of porosity due to the capture of gas bubbles.

3. The high content of hydrogen in the column of the electric arc, molten metal in the

transfer and in weld pool, which results in hydrogen capture in the metal of the weld

and in the heat-affected zone. This increases the susceptibility to the appearance of

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cold cracks, brings about porosity and degrades the mechanical properties of the joint.

4. The high oxygen content in the electric arc column, molten metal in the transfer and

weld pool, which leads to oxidation, reduction of the proportion of alloy elements and

the degradation of mechanical properties.

5. The disintegration and solving of the coating of the electrodes, which results in

electric arc instability and the appearance of porosity.

Fig 2; figure shows person doing underwater welding in ocean

2.1.5 Reactions caused during welding

The dissociation of water in the case of wet underwater welding is carried out according to

reaction (1) and the partial pressures of hydrogen and oxygen in the electric arc increase:

2H2O ® 2H2 + O2 (1)

In addition, the carbon which partially emerges from the combustion of the electrode coating

and oxygen create carbon dioxide, which also dissociates, according to reaction (2):

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2CO2 ® 2CO + O2 (2)

According to these reactions, through the evaporation and dissociation of water and the

combustion of the coating, the following gases are created:

· 62-82% H2 (hydrogen) · 11-24% CO (carbon monoxide)

· 4-6% CO2 (carbon dioxide)

· O2 (oxygen)

· N2 (nitrogen)

Because of the rapid cooling, locally quenched structures of great hardness are formed in the

welded joint. Their hardness reading sometimes exceeds 350 HV10 in the heat affected zone.

In addition, the high proportion of diffusible hydrogen, which ranges from 30 to 80 ml

H2/100g of the weld metal, makes such a structure susceptible to the appearance of hydrogen

brittleness, i.e. it leads to the incidence of cold cracks caused by hydrogen.

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Fig 3; Tip of rutile underwater wet welding electrodes with double waterproof

coatingThe acceptability of the base material for wet underwater welding is defined on the basis of

determining the CE- carbon equivalents, according to the standard AWS D3.6M:1999:

Specification for underwater welding according to the following expression:

CE = C +Mn

+Cr + Mo + V

+Ni + Cu

6 5 15

Fig 4; Underwater wet welding in the laboratory pool

2.1.6 Engineering materials used for wet welding

Engineering steels with less than 0,1% C and steels with carbon equivalent smaller than 0,4%

are suitable for Wet underwater welding. Steels with carbon equivalent greater than 0,4%

have high sensitivity to hydrogen Induced cold cracking (HICC) and can be wet underwater

welded only if special welding filler material and Welding techniques are used. When

welding involves steels with carbon equivalent CE greater than 0,4%, the heat affected zone

of the base Material is sensitive to hydrogen-induced cold cracking and to undesired high

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hardness. In underwater dry welding, it is possible to implement pre-heating and maintenance

of inter-layer temperature in order to reduce the humidity volume.

2.1.7 Welding process and consumables

Underwater manual metal arc wet welding is the oldest technique for joining metals

underwater. It is applicable for the repair of both ship hulls and underwater structures but is

considered a second-rate technology because of the poor mechanical characteristics of the

welded joint. Today, wet underwater welding has an important Industrial, commercial and

economic potential in the development and maintenance of underwater structures and

because of the much lower costs and better flexibility has an advantage over dry underwater

welding Techniques, high quality welds also being achieved. However, further development

of the steels used in underwater structures, the large number of installed and planned

pipelines and increasing depth require further Development of the procedure of underwater

wet welding. Clearly in this the MMAW technology is facing the major barrier of automation

solutions, which restricts it to use at lower depths, down to 60 m, while other Welding

techniques like FCAW are becoming of primary importance for further research.

Professionally skilled and educated diver-welders are cornerstone of underwater welding

activities. It is noticed that incorrect working technique increase hydrogen level in weld

metal, as well as quantity of porosity. Also, bad electrode angle and higher welding speed are

influencing significantly on slag inclusion, what is well known problem in underwater wet

welding. Measuring of weld hydrogen content showed that apart from Welding position, type

of electrode coating etc., welding technique is very important tool in decreasing diffused

hydrogen amount.

Further, good quality stick electrodes are needed to establish and maintain electric arc and to

deposit weld metal. So far, developed coated electrodes are very good in their operational

characteristics. Especially, it is of crucial impact that coating provides easy slag removal and

low level of hydrogen as possible. It should be noted that, apart from actually reducing the

current amperage, possible chemical Aggressiveness of water could damage the compactness

of coating causing it to degrade and reduce arc stability or even extinguish the arc.

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Formulation of the coating is especially important. Increased weld joint properties can be

achieved by coating Modifications with additives for the improvement of arc stability or to

reduce hydrogen content. For Decreasing of hydrogen, special welding procedures are

needed to extend the cooling time and to perform heat treatment on the previous deposited

bead. For higher strength steels, investigations are conducted with Stainless Steel and Ni-

based electrodes. Electrodes with double coating have proven very good, especially because

of high-quality coatings that prevent penetration of water and degrading of the coating, thus

maintaining the quality of the weld.

2.1.8 Equipment for underwater wet weldingThe equipment used for underwater wet welding has been combined with certain

modifications, from the diving and welding equipment. The underwater wet welding

equipment has to meet all the safety aspects, and at the same time the diver-welder has to be

provided with satisfactory operating conditions because of the limited time spent under water

and the efficiency of the very process, and it has to be regularly maintained according to

stipulated regulations in order to prolong its life-cycle and insure its proper functioning in

working conditions. Depending on the requirements set by the task it is possible to use also

additional equipment such as special devices for holding and centering the work pieces or

e.g. heated suits in case of colder climates. The supporting team takes care of providing

entrance into the water, communication, air supply, tools and electrodes supply, regulation of

welding parameters as well as of other safety elements.

The organization of work plays a big role in implementing the working activities, and

everything is carried out according to a pre-arranged plan and protocol. In case of connection

break-up or unforeseen circumstances, the diver comes out of the water in order to avoid

possible incident situations.

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Fig 5;Underwater joint made with arc “spot” welding. Fig 6; Appearance of the

Welded shape

2.1.9 Advantages of Wet WeldingWet underwater MMA welding has now been widely used for many years in the repair of

offshore platforms. The benefits of wet welding are: -

1) The versatility and low cost of wet welding makes this method highly desirable.

2) Other benefits include the speed. With which the operation is carried out.

3) It is less costly compared to dry welding.

4) The welder can reach portions of offshore structures that could not be welded using other

methods.

5) No enclosures are needed and no time is lost building. Readily available standard welding

machine and equipment’s are used. The equipment needed for mobilization of a wet

welded job is minimal.

Disadvantages of Wet Welding Although wet welding is widely used for underwater fabrication works, it suffers from the

Following drawbacks;-

1) There is rapid quenching of the weld metal by the surrounding water. Although

quenching increases the tensile strength of the weld, it decreases the ductility and impact

strength of the weldment and increases porosity and hardness.

2) Hydrogen Embrittlement – Large amount of hydrogen is present in the weld region,

resulting from the dissociation of the water vapour in the arc region. The H2 dissolves in

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the Heat Affected Zone (HAZ) and the weld metal, which causes Embrittlement, cracks

and microscopic fissures. Cracks can grow and may result in catastrophic failure of the

structure.

3) Another disadvantage is poor visibility. The welder sometimes is not able to weld

properly.

3. Dry welding (hyperbaric welding)

Hyperbaric welding is carried out in chamber sealed around the structure to be welded. The

chamber is filled with a gas (commonly helium containing 0.5 bar of oxygen) at the

prevailing pressure. The habitat is sealed onto the pipeline and filled with a breathable

mixture of helium and oxygen, at or slightly above the ambient pressure at which the welding

is to take place. This method produces high-quality weld joints that meet X-ray and code

requirements. The gas tungsten arc welding process is employed for this process. The area

under the floor of the Habitat is open to water. Thus the welding is done in the dry but at the

hydrostatic pressure of the sea water surrounding the Habitat.

Dry welding in underwater may be achieved by several ways;

a. Dry habitat welding; Welding at ambient water pressure in a large chamber from which

water has been displaced, in an atmosphere such that the welder/diver does not work in

diving gear. This technique may be addressed as dry habitat welding.

b. Dry chamber welding; Welding at ambient water pressure in a simple open-bottom dry

chamber that accommodates the head and shoulders of the welder/diver in full diving

gear.

c. Dry spot welding; Welding at ambient water pressure in a small transparent, gas filled

enclosure with the welder/diver in the water and no more than the welder/diver’s arm in

the enclosure.

d. Dry welding at one atmosphere; Welding at a pressure vessel in which the pressure is

maintained at approximately one atmosphere regardless of outside ambient water

pressure.

e. Cofferdam welding; Welding inside of a closed bottom, open top enclosure at one

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atmosphere.

Underwater welding in a dry environment is made possible by encompassing the area to be

welded with a Physical barrier (weld chamber) that excludes water. The weld chamber is

designed and custom built to Accommodate braces and other structural members whose

centerlines may intersect at or near the area that is to be welded. The chamber is usually built

of steel, but plywood, rubberized canvas, or any other suitable Material can be used. Size and

configuration of the chamber are determined by dimensions and geometry of the area that

must be encompassed and the number of welders that will be working in the chamber at the

same time. Buoyancy of the chamber is offset by ballast, by mechanical connections and

chamber to the structure, or by a combination of both.

3.1 Dry welding in a habitat; welding at ambient pressure in a large chamber from

which water was displaced and where such atmosphere is achieved that welder has no need

to use diving equipment. As it is shown on the figure 11 welders are completely in dry

environment and weld properties are equivalent to one welded in normal conditions.

However, much more fit-up time is necessary to fix the habitat and prepare it for welding.

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Fig 7; specially designed habitat for repair of K-nodeon offshore platform

3.2 Dry chamber welding; welding at ambient pressure in a simple open bottomed dry

chamber that at least accommodates the head and shoulders of a diver-welder in full diving

equipment. Welder-diver is partly immersed in water but welding is performed in a dry

atmosphere. Habitat is smaller and less complex than in case of dry habitat welding. Due to

smaller size of habitat other operating facilities are also less expensive.

Fig 8; dry welding in minihabitat where the diver-welder is partially immersed in water

3.3 Advantages of Dry Welding1) Welder/Diver Safety – Welding is performed in a chamber, immune to ocean currents

and marine animals. The warm, dry habitat is well illuminated and has its own

environmental control system (ECS).

2) Good Quality Welds – This method has ability to produce welds of quality

comparable to open air welds because water is no longer present to quench the weld

and H2 level is much lower than wet welds.

3) Surface Monitoring – Joint preparation, pipe alignment, NDT inspection, etc.

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are monitored visually.

4) Non-Destructive Testing (NDT) – NDT is also facilitated by the dry habitat

environment.

Disadvantages of Dry Welding1) The habitat welding requires large quantities of complex equipment and much support

equipment on the surface. The chamber is extremely complex.

2) 2) Cost of habitat welding is extremely high and increases with depth. Work depth

has an effect on habitat welding. At greater depths, the arc constricts and corresponding

higher voltages are required. The process is costly – an $80000 charge for a single weld

job. One cannot use the same chamber for another job, if it is a different one.

4. RISKS INVOLVED

There is a risk to the welder/diver of electric shock. Precautions include achieving adequate

electrical insulation of the welding equipment, shutting off the electricity supply

immediately the arc is extinguished, and limiting the open-circuit voltage of MMA (SMA)

welding sets. Secondly, hydrogen and oxygen are produced by the arc in wet welding.

Precautions must be taken to avoid the build-up of pockets of gas, which are potentially

explosive. The other main area of risk is to the life or health of the welder/diver from

nitrogen introduced into the blood steam during exposure to air at increased pressure.

Precautions include the provision of an emergency air or gas supply, stand-by divers, and

decompression chambers to avoid nitrogen narcosis following rapid surfacing after saturation

diving.

For the structures being welded by wet underwater welding, inspection following welding

may be more difficult than for welds deposited in air. Assuring the integrity of such

underwater welds may be more difficult, and there is a risk that defects may remain

undetected.

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Fig 9; ARRANGEMENTS OF UNDERWATER WELDING

5. APPLICATION OF UNDERWATER WELDING:

(a) Offshore construction for tapping sea resources.

(b) Temporary repair work caused by ship’s collisions or unexpected accidents.

(c) Salvaging vessels sunk in the sea.

(d) Repair and maintenance of ships.

(e) Construction of large ships beyond the capacity of existing docks.

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Fig 10; electrodes used in underwater welding

6. Safety and diving issues

Hazards during underwater welding can be divided into hazards that are a consequence of

welding and hazards that are a consequence of diving. The welding hazards are dangers from

electrical current, explosions and electric arc flashes. Diving dangers are the dangers that are

possible in any dive, such as the sudden emergence of the diver onto the surface, toxic effects

of pressurized oxygen, the toxic effects of carbon dioxide, the narcotic effects of nitrogen,

hypoxia, decompression sickness, baro-traumatic gas embolisms, drowning, contamination of

the diver’s air, injuries during the dive, risk of infection, hypo-and hyperthermia.

Hazards arising from welding operations

During underwater welding there are many potential difficulties that if ignored can bring

about major injuries or even death. The greatest hazard in underwater wet welding is

electricity. Alternate current is not used during underwater welding. An electric shock arising

from alternating current results in spasms of the muscles, and the diver who has electrodes in

his hand cannot in such a situation drop them since he is inside an electric circuit. During

underwater welding, only direct current is used. Appropriate welding power sources have to

ensure good welding parameters. Welding power sources are constructed in such a way that

they have reduced voltage, for the safety of the welder, and yet also appropriate

characteristics for welding. Transistor welding power sources are also used, and further

research suggests that the current stage of welding power source technology will enable a

better establishment of the electric arc and its stability. As a result of welding and the

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creation of drops of molten metal it is possible to damage the dry diver suit. Even the

smallest of holes in a dry diver suit will lead to the leakage of water into the suit, increasing

the danger from electric shocks. The second direct hazard consists of explosions that can

happen during underwater welding and cutting.

7. Developments in Under Water WeldingWet welding has been used as an underwater welding technique for a long time and is still

being used. With recent acceleration in the construction of offshore structures underwater

welding has assumed increased importance. This has led to the development of alternative

welding methods like friction welding, explosive welding, and stud welding. Sufficient

literature is not available of these processes.

Scope for further developmentsWet MMA is still being used for underwater repairs, but the quality of wet welds is poor and

are prone to hydrogen cracking. Dry Hyperbaric welds are better in quality than wet welds.

Present trend is towards automation. THOR – 1 (TIG Hyperbaric Orbital Robot) is developed

where diver performs pipefitting, installs the trac and orbital head on the pipe and the rest

process is automated.

Developments of diver less Hyperbaric welding system is an even greater challenge calling

for annexe developments like pipe preparation and aligning, automatic electrode and wire

reel changing functions, using a robot arm installed. This is in testing stage in deep waters.

Explosive and friction welding are also to be tested in deep waters.

8. CONCLUSIONSWet welding is still being used for underwater repairs, but the quality of wet welding is poor

than dry welding. But the dry welding is costlier than wet welding.

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Underwater welding is mostly employed in marine engineering products –in installations of

oil and gas rigs. Underwater welding can be classified depending upon the types of

equipment’s and the types of procedures involved. The most common underwater welding

process, known as manual metal arc building (MMA), is employed for deep water repairing

activities.

Cofferdam welding process and Hyperbaric welding process are normally carried out for

underwater welding operations. They are employed for welding steel pipelines, other

offshore structures, submerged parts of large ships and underwater structures supporting a

harbour. The safety measures include emergency air or gas supply, stand-by divers and

decompression chambers.

REFERENCES

1) D. J Keats, Manual on Wet Welding. 2) Annon, Recent advances in dry underwater pipeline welding, Welding Engineer, 1974.

3) Lythall, Gibson, Dry Hyperbaric underwater welding, Welding Institute.

4) W.Lucas, International conference on computer technology in welding. 5) Stepath M. D, Underwater welding and cutting yields slowly to research, Welding

Engineer, April 1973.

6) Silva, Hazlett, Underwater welding with iron – powder electrodes, Welding Journal, 1971.

7) Blakemore, G. R. (2000): Underwater Intervention 2000 – Houston, Jan 24-26.

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